In the United States and many other countries possessed of abundant timber resources, wood has always been an important construction material. Its good availability, low heat conductivity, and sound-deadening qualities, have made it an outstanding building material since early human history.
Rail transportation of freight and passenger cars is an important part of the world's infrastructure. This is especially true in heavily urban areas in North America and Europe and also in large geographical areas, such as the United States and Canada. Most cities in developed countries of the world contain hundreds, if not thousands, of miles of railway track. Indeed, a large and developed country, such as the United States, might contain several hundred thousand miles of railway track, including main lines, marshalling yards, commuter lines, and so on.
Most types of railway tracks are supported on a plurality of individual ties spaced one from another along the length of the railway track. The ties are typically about two and one-half meters long and about fifteen to twenty centimeters in width and thickness. The rails are secured to the ties in any one of a variety of ways, such as by means of large spikes, or by means of specially designed clips engaging co-operating clip receiving members embedded in the ties. The ties keep the rails spaced apart at a predetermined distance. The ties are further designed to carry the static and dynamic loads of freight and passenger trains traveling at various speeds, including relatively high speeds, perhaps well in excess of one hundred miles per hour. Such ties include wood ties, concrete ties, plastic encapsulated wood ties, plastic composite ties, and steel ties.
The most common type of railway tie is a conventional wood tie. Wood railway ties are the preferred railway ties in North America, for instance, since they can stand climatic change and are relatively low cost to purchase and initially install, when compared to other types of railway ties. In use, wood railway ties are supported and somewhat surrounded by a compacted granular bed known as ballast. The ties tend to shift in the ballast bed, due to the extreme dynamic loading on the railroad track by a passing train. Wood railway ties therefore require routine maintenance in order to ensure that they are properly supporting the railway track rails. Also, the ballast bed requires consistent and regular maintenance in order to keep the individual pieces of ballast in place.
Because wood is a cellulosic material, it is susceptible to decay and deterioration over any extended period of time. Decay is, in part, due to biological attacks by microorganisms (such as fungi and bacteria), marine borers, and insects. Much of the decay of wood in service is inevitable. It is particularly severe as a result of the activities of low forms of plants known as wood-destroying fungi. This type of fungi often causes extensive damage and financial loss to buildings.
The conditions necessary for the development of decay-producing fungi in wood are: (1) a supply of suitable wood, (2) a sufficient amount of moisture, (3) at least a small amount of air, and (4) a favorable temperature. A deficiency in any of these requirements may inhibit the growth of a fungus and may reduce the decay of wood. Under normal service conditions of wood, the deficiency is difficult to maintain. Therefore, various techniques of wood preservation have been developed, including surface coating, surface treating, and pressure penetration of the wood with a variety of wood preservatives. There are generally two types of wood preservatives: oil-borne preservatives and water-borne preservatives. Oil-borne preservatives include, for example, creosote, pentachlorophenol, copper naphthenate, zinc naphthenate, copper-8-quinolinolate, and others. Important water-borne preservatives are arsenic salts, boric acid, chromium salts, chromated zinc chloride, copper sulfate, mercuric chloride, sodium pentachlorophenate, zinc sulfate, chromated copper arsenate, etc.
Creosote has been used for decades to treat wood railway ties in order to protect the wood railway ties from insects, rotting, and so on. Generally, creosote-treated wood railway ties last about 30 years in northern climates. But their life is shortened to about 15 years at the longest in southern climates. As a general rule, the further south, the shorter the life expectancy for creosote-treated wood railway ties. This is due to the relatively high humidity and temperatures in the southern climates. For these reasons, there is need for a creosote-based wood treatment composition which would prolong the useful life of a wood product, especially in a southern climate.